This invention relates to the production of substituted aromatic azo compounds. In one aspect, this invention relates to the production of substituted aromatic amines. In another aspect, this invention relates to the production of 4-aminodiphenylamine (4-ADPA) or substituted derivatives thereof. In another aspect, this invention relates to the preparation of alkylated p-phenylenediamines or substituted derivatives thereof useful as antioxidants from the substituted aromatic amines, such as 4-ADPA or substituted derivatives thereof.
It is known to prepare substituted aromatic amines by way of a nucleophilic aromatic substitution mechanism wherein an amino functional nucleophile replaces halide. For example, it is known to prepare 4-ADPA by way of a nucleophilic aromatic substitution mechanism, wherein an aniline derivative replaces halide. This method involves preparation of a 4-ADPA intermediate, namely 4-nitrodiphenylamine (4-NDPA) followed by reduction of the nitro moiety. The 4-NDPA is prepared by reacting p-chloronitrobenzene with an aniline derivative, such as formanilide or an alkali metal salt thereof, in the presence of an acid acceptor or neutralizing agent, such as potassium carbonate, and, optionally, utilizing a catalyst. See, for example, U.S. Pat. Nos. 4,187,248; 4,683,332; 4,155,936; 4,670,595; 4,122,118; 4,614,817; 4,209,463; 4,196,146; 4,187,249; 4,140,716. This method is disadvantageous in that the halide that is displaced is corrosive to the reactors and appears in the waste stream and must therefore be disposed of at considerable expense. Furthermore, use of an aniline derivative such as formanilide, and use of p-chloro-nitrobenzene, requires additional manufacturing equipment and capabilities to produce such starting materials from aniline and nitrobenzene, respectively.
It is also known to prepare 4-ADPA from the head-to-tail coupling of aniline. See, for example, G.B. 1,440,767 and U.S. Pat. No. 4,760,186. This method is disadvantageous in that the yield of 4-ADPA is not acceptable for a commercial process. It is also known to decarboxylate a urethane to produce 4-NDPA. See U.S. Pat. No. 3,847,990. However, such method is not commercially practical in terms of cost and yield.
It is known to prepare 4-ADPA by hydrogenating p-nitrosodiphenylhydroxylamine which can be prepared by catalytic dimerization of nitrosobenzene utilizing, as a reducing agent, aliphatic compounds, benzene, naphthalene or ethylenically unsaturated compounds. See, for example, U.S. Pat. Nos. 4,178,315 and 4,404,401. It is also known to prepare p-nitrosodiphenylamine from diphenylamine and an alkyl nitrate in the presence of excess hydrogen chloride. See, for example, U.S. Pat. Nos. 4,518,803 and 4,479,008.
Aromatic amide bonds are currently formed by the reaction of an amine with an acid chloride. This method of forming aromatic amide bonds is also disadvantageous in that chloride is displaced which is corrosive to the reactors, and appears in the waste stream from which it must be removed at considerable expense. A nonhalide process which produces aromatic amide bonds in the substituted aromatic amines would eliminate these problems.
The process of the invention is a nonhalide process for preparing substituted aromatic azo compounds and substituted aromatic amines and therefore eliminates the expensive halide removal from the waste stream as well as corrosion problems caused by the halide. In addition, substituted aromatic azo compounds and substituted aromatic amines containing aromatic amide bonds can be prepared by the process of the invention. Furthermore, the process of the invention is more economical than current commercial routes and is simpler in that, in one embodiment, substituted aromatic amines, such as 4-ADPA or substituted derivatives thereof, are produced directly without the need of a separate reduction step.